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The Azotobacter vinelandii AlgE mannuronan C‐5‐epimerase family is essential for the in vivo control of alginate monomer composition and for functional cyst formation
Author(s) -
Steigedal Magnus,
Sletta Håvard,
Moreno Soledad,
Mærk Mali,
Christensen Bjørn E.,
Bjerkan Tonje,
Ellingsen Trond Erling,
Espìn Guadalupe,
Ertesvåg Helga,
Valla Svein
Publication year - 2008
Publication title -
environmental microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.954
H-Index - 188
eISSN - 1462-2920
pISSN - 1462-2912
DOI - 10.1111/j.1462-2920.2008.01597.x
Subject(s) - azotobacter vinelandii , biology , in vivo , microbiology and biotechnology , monomer , cyst , biochemistry , genetics , bacteria , nitrogen fixation , nitrogenase , medicine , chemistry , organic chemistry , radiology , polymer
Summary The industrially widely used polysaccharide alginate is a co‐polymer of β‐ d ‐mannuronic acid and α‐ l ‐guluronic acid (G), and the G residues originate from a polymer‐level epimerization process catalysed by mannuronan C‐5‐epimerases. In the genome of the alginate‐producing bacterium Azotobacter vinelandii genes encoding one periplasmic (AlgG) and seven secreted such epimerases (AlgE1–7) have been identified. Here we report the generation of a strain (MS163171) in which all the algE genes were inactivated by deletion ( algE1–4 and algE6–7 ) or interruption ( algE5 ). Shake flask‐grown MS163171 produced a polymer containing less than 2% G ( algG still active), while wild‐type alginates contained 25% G. Interestingly, addition of proteases to the MS163171 growth medium resulted in a strong increase in the chain lengths of the alginates produced. MS163171 was found to be unable to form functional cysts, which is a desiccation‐resistant differentiated form developed by A. vinelandii under certain environmental conditions. We also generated mutants carrying interruptions in each separate algE gene, and a strain containing algE5 only. Studies of these mutants indicated that single algE gene inactivations, with the exception of algE3 , did not affect the fractional G content much. However, for all strains tested the alginate composition varied somewhat as a response to the growth conditions.